Foamable polyorganosiloxane compositions

ABSTRACT

Polyorganosiloxane foams are prepared by the volatilization of a blowing agent within a polyorganosiloxane composition that is curable by a hydrosilation reaction and includes as a foam stabilizer a resinous polyorganosiloxane comprising trimethylsiloxy units, SiO 4/2  units and a specified class of fluorine-containing siloxane units.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the preparation of polyorganosiloxane foams.More particularly, this invention relates to polyorganosiloxanecompositions that are converted to useful cured foams when theingredients of the composition, including a blowing agent, are combinedand dispensed into an area under atmospheric pressure at temperature ofabout 0° C. or higher.

2. Background Information

A number of different methods for generating curable polyorganosiloxanefoams are disclosed in the prior art. One of these methods employs thereaction of silicon-bonded hydrogen atoms with a source of hydroxylgroups such as water, alcohols or polyorganosiloxanes containingsilicon-bonded hydroxyl groups. This reaction generates hydrogen gasthat functions as the blowing agent. The use of internally generatedhydrogen as a blowing agent for polyorganosiloxane foams is disclosed inU.S. Pat. No. 3,923,705, issued to Smith on Dec. 2, 1975, in U.S. Pat.No. 4,026,842, issued to Lee and Ronk on May 31, 1977 and in U.S. Pat.No. 4,026,844, issued to Kittle and Ronk on May 31, 1977.

Production of foams by stirring air or other gas into a curablepolyorganosiloxane composition containing silicon-bonded vinyl radicalsand silicon-bonded hydrogen atoms is disclosed in U.S. Pat. No.4,368,279, issued to Modic and Boudreau, on Jan. 11, 1983. In accordancewith the method described in this patent, the polyorganosiloxanecomposition is mixed in the presence of the gaseous blowing agent andthen placed in a vacuum chamber and maintained under a vacuum of atleast 600 mm of mercury until the foam cures sufficiently to becomeself-supporting, which requires at least five minutes. Patentees teachthat collapse of the foam occurs in the absence of vacuum, and thattheir method is limited to producing foamed slab stock in a factory, andcannot be applied to producing foam in a conduit, between inner andouter structural walls or other locations where a foam is generated atthe installation site.

The advantage of packaging in a single portable container all of theingredients, including blowing agent required to produce apolyorganosiloxane foam has been recognized. U.S. Pat. No. 4,229,548,issued on Oct. 21, 1980 to Sattleger et al. discloses a 2-compartmentaerosol type container for storing and dispensing a foamablepolyorganosiloxane composition. The container consists of a flexiblewalled inner compartment containing a foamable, room temperaturevulcanizable (RTV) composition that includes a hydroxy-endblockedpolydiorganosiloxane, a curing agent and, optionally, a gaseous blowingagent and an outer compartment containing a moisture free inert gasunder a pressure of from 0.2 to 3.0 megapascals. The container isequipped with a valve through which the foamable composition isdispensed under the pressure of the gas confined in the outercompartment of the container. The formation of polyorganosiloxane foamsby dispensing a one-part moisture curable RTV polyorganosiloxanecomposition stored under pressure in a 2-compartment container is alsotaught in German published application Nos. 2,909,443 and 2,911,971.

Foams produced by dispensing RTV polyorganosiloxane compositions,including a blowing agent and/or a propellant, from pressurizedcontainers, such as aerosol cans, are typically of relatively poorquality and characterized by average cell sizes larger than 2 mm.,densities from 0.48 to 0.81 g./cc and relatively low foam height due todrainage of uncured or partially cured liquid from the cellularstructure of the foam during the curing process. The need to minimizecollapse of partially cured foams by the use of vacuum, by heating toaccelerate curing, by the addition of fillers or other means requiringadditional processing steps may more than offset the advantages achievedby using foamable compositions packaged in portable pressurizedcontainers such as aerosol cans.

Various additives have been used to reduce the density ofpolyorganosiloxane foams. One such additive is a resinous organosiloxanecopolymer containing repeating units of the formulae R₃ SiO_(1/2) andSiO_(4/2), where R represents alkyl, aryl, aralkyl, alkaryl, cycloalkyl,vinyl, allyl or fluoroalkyl and the molar ratio of R₃ SiO_(1/2) toSiO_(4/2) units is from 0.25 to about 0.8:1. This type of additive isdisclosed in U.S. Pat. No. 4,418,157, which issued to Modic on Nov. 29,1983.

Kim, Lee and Ronk in U.S. Pat. No. 4,026,845, issued on May 31, 1977,teach the addition of fluorinated surfactants to reduce the density offoams generated by the hydrogen produced during the reaction ofsilicon-bonded hydroxyl groups with silicon-bonded hydrogen atoms in thepresence of a platinum-containing catalyst. It has now been found thatthese fluorinated surfactants will not stabilize the cellular structureof partially cured polyorganosiloxane foams dispensed from pressurizedcontainers in the absence of large amounts of solid fillers.

An objective of this invention is to provide foamable polyorganosiloxanecompositions that are curable by a hydrosilation reaction, can bepackaged in pressurized containers and when dispensed from thesecontainers form useful foams. A second objective of this invention is toprovide one-part foamable compositions that cure in the presence ofmicrowave radiation.

SUMMARY OF THE INVENTION

It has now been found that the stability of uncured and partially curedfoams prepared by volatilization of a blowing agent within apolyorganosiloxane composition that is curable by a hydrosilationreaction is substantially improved by including in said composition aresinous polyorganosiloxane comprising trimethylsiloxy units, SiO_(4/2)units and a specified class of fluorine-containing siloxane units.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a foamable polyorganosiloxane compositionexhibiting a viscosity of at least 0.5 Pa.s at 25° C., said compositionconsisting essentially of the product obtained by homogeneously blendingtogether (A) a polydimethylsiloxane containing at least two vinylradicals per molecule and exhibiting a viscosity of from 0.1 to 100 Pa.sat 25° C.; (B) an organohydrogensiloxane containing an average of atleast 3 silicon-bonded hydrogen atoms per molecule in an amountsufficient to cure said composition in the presence of a hydrosilationcatalyst, (C) a catalytically effective amount of a platinum- orrhodium-containing hydrosilation catalyst, (D) from 0.2 to 25%, based onthe weight of said polyorganosiloxane composition, of a foam stabilizerconsisting essentially of a resinous, benzene-soluble organosiloxanecopolymer comprising SiO_(4/2) units, (CH₃)₃ SiO_(1/2) units andfluorine-containing units selected from the group consisting of R_(a)R.sub. 'SiO(_(4-a-b))/ 2, R"[Si(R')_(b) O.sub.(3-b)/2 ]₂ andcombinations thereof, where R is a monovalent organic radical containingat least four perfluorinated carbon atoms, R' is an alkyl radicalcontaining from 1 to 3 carbon atoms, R" is a divalent organic radicalcontaining at least four perfluorinated carbon atoms, R and R" arebonded to the silicon atoms of their respective fluorine-containingunits by means of a sequence of at least two methylene radicals or asilicon bonded oxygen atom that is, in turn, bonded to a sequence of atleast two methylene radicals, a is 1 or 2, b is 0, 1 or 2 and the sum ofa and b is 3 or less, the molar ratio of all units other than hydroxyland said SiO_(4/2) units to said SiO_(4/2) units is from 0.7:1 to 1.1:1inclusive, and the molar ratio of the (CH₃)₃ SiO_(1/2) units withrespect to said fluorine-containing units and any remaining units otherthan said SiO_(4/2) units is such that (a) the surface tension exhibitedby a 10% weight percent solution of (D) in a trimethylsiloxy endblockedpolydimethylsiloxane exhibiting a viscosity of 0.01 Pa.s at 25° C. isless than 2.2×10⁻⁴ newtons per cm at 25° C., and (b) said 10% weightpercent solution requires the addition of from 0 to 100 weight percentof xylene to achieve clarity at 25° C.; (E) an amount of a blowing agentsufficient to convert said composition to a foam when said compositionis under atmospheric pressure at a temperature of at least 0° C.; (F)optionally, an amount of a catalyst inhibitor sufficient to deactivatesaid platinum-containing hydrosilation catalyst at temperatures up to50° C.; and (G) optionally, an amount of a microwave sensitive materialsufficient to generate the heat required to activate said hydrosilationcatalyst in the presence of said inhibitor (F) and microwave radiation.

Polydimethylsiloxanes suitable for use as ingredient (A) of the presentcompositions contain at least two vinyl radicals per molecule andexhibit a viscosity of from 0.05 to 100 Pa.s at 25° C. Preferably thevinyl radicals are located at the terminal positions and the viscosityis from 0.1 to 50 Pa.s.

In addition to dimethylsiloxane units, (A) can include small amounts oftrimethylsiloxy, monomethylsiloxane, methylvinylsiloxane and SiO_(4/2)units that can result from impurities in the intermediates used toprepare (A). Typically these units constitute less than 0.5 percent byweight of (A). Ingredient (A) can also contain diorganosiloxane unitscontaining hydrocarbon radicals or substituted hydrocarbon radicalsother than methyl or vinyl, such as ethyl, propyl, 3,3,3-trifluoropropyland/or phenyl, so long as these radicals do not interfere with theability of the foam stabilizer to minimize collapse of the partiallycured foam. Most preferably the terminal units of (A) aredimethylvinylsiloxy units, this preference being based on theavailability of the corresponding intermediates and the reactivity ofthe vinyl group.

Ingredient (A) can be a monodisperse polydimethylsiloxane or a blend oftwo or more polydimethylsiloxanes of different molecular weight, andpreferably constitutes from 40 to 85% by weight of the foamablecomposition.

The organohydrogensiloxane, referred to hereinafter as ingredient (B),reacts with the vinyl radicals of ingredient (A) to form a curedcomposition. Organohydrogensiloxanes containing at least 3silicon-bonded hydrogen atoms per molecule and no more than one hydrogenper silicon atom are known materials, and are disclosed, for example, byPolmanteer et al. in U.S. Pat. No. 3,697,473, issued on Oct. 10, 1972and in U.S. Pat. No. 3,989,668, issued on Nov. 2, 1976 to Lee et al.These patents are incorporated herein by reference as examples of knownorganohydrogensiloxanes. Ingredient (B) includes homopolymers,copolymers and mixtures thereof, and can contain repeating units of theformulae R*HSiO, R*₂ HSiO, and/or HSiO_(3/2) in addition to units of theformulae R*₃ SiO, R*₂ SiO, R*SiO_(3/2) and/or SiO_(4/2). In theseformulae R* represents a hydrocarbon or halohydrocarbon radical thatdoes not contain ethylenic unsaturation. R* can be alkyl, haloalkyl,cycloalkyl, aryl, alkaryl or aralkyl. To ensure that theorganohydrogensiloxane is compatible with ingredient (A), at least 80%,most preferably 100%, of the R* radicals are methyl.

Examples of preferred organohydrogensiloxanes include cyclicpolymethylhydrogensiloxanes, copolymers containing dimethylsiloxane andmethylhydrogensiloxane units and trimethylsiloxy endblockedpolymethylhydrogensiloxanes. Ingredient (B) preferably contains from 0.5to about 1.6 weight percent of silicon-bonded hydrogen atoms. Mostpreferably the organohydrogensiloxane contains an average of at leastfour silicon-bonded hydrogen atoms per molecule.

A second preferred type of organohydrogensiloxane is represented by thegeneral formula (HR₂ ^(*) SiO)₄ Si, wherein R* is as definedhereinabove. The species wherein R* represents methyl is particularlypreferred because of the rapid reaction rate of this compound withingredient (A). Using a more reactive organohydrogensiloxane is onemethod for minimizing the extent to which a foam collapses duringcuring.

Ingredient (B) is preferably a liquid to facilitate blending withingredient (A). The concentration of ingredient (B) should be sufficientto provide from 1 to 3 silicon-bonded hydrogen atoms per silicon-bondedvinyl radical present in the foamable composition.

The hydrosilation reaction between ingredients (A) and (B) of thepresent foamable composition is catalyzed by a platinum- orrhodium-containing material referred to hereinafter as ingredient (C).

Any of the known platinum-containing hydrosilation catalysts willpromote curing of foams prepared using the compositions of thisinvention. Many of these catalysts are active at temperatures of from 25to 50° C. To minimize drainage of liquid from partially cured foams andthe accompanying increase in foam density, the curing reaction should beas rapid as possible, particularly for those compositions exhibitingviscosities in the lower portion of the preferred range of from 0.5 to100 Pa.s at 25° C. Catalysts yielding the most rapid curing rate at roomtemperature are complexes formed by reacting chloroplatinic acid with avinyl-terminated polydiorganosiloxane of the general formula (CH₂ ═CH)R₂'"Si[OSi(CH₃)(R'")]_(x) OSiR₂ '"(CH═CH₂) where each R'" is individuallyselected from the group consisting of alkyl radicals containing from 1to 4 carbon atoms, phenyl radicals and 3,3,3-trifluropropyl radicals andx is an integer from 1 to 6, inclusive. Catalysts of this type aredescribed in U.S. Pat. No. 3,419,593, issued to Willing on Dec. 31, 1968and is incorporated herein in its entirety by reference thereto.

The platinum containing catalyst is present in an amount sufficient tocatalyze curing of the foamable composition at a sufficiently rapid ratethat will minimize, if not eliminate, the drainage of liquid reactantsand the resultant collapsing of the foam. Typically the catalystconcentration is equivalent to more than about 0.1 by weight of platinumper million parts by weight of foamable composition. Preferably theplatinum concentration is between about 5 and 20 parts per million partsof the total composition. Higher catalyst concentrations apparently donot serve any useful purpose unless it is desired to impart flameretardancy to the final foam. The use of 50 ppm or more of platinum as aflame retardant for polyorganosiloxanes is known.

Rhodium-containing catalysts suitable for use in heat curablecompositions include those disclosed in U.S. Pat. No. 4,026,835, issuedto Lee and Ronk on May 31, 1977, and is incorporated in its entirety byreference thereto. The catalysts described in this patent are complexescontaining at least one chlorine atom in addition to a specified groupof phosphorous- or sulfur-containing ligands. All of these complexes areknown in the art. Rhodium catalysts are typically inactive atconventional temperatures of 25° to 40° C., but promote a rapidhydrosilation reaction at temperatures of about 50° C. and above. Thesecatalysts are preferred for use in one-part, heat-curable foamablecompositions that constitute part of the present invention and aretypically used at the same concentrations as platinum-containingcatalysts.

The foam stabilizer, referred to hereinafter as ingredient (D),maintains the cellular structure of the froth produced by dispensing afoamable composition of this invention from its storage container(s)until the froth has cured sufficiently to become self supporting. In theabsence of ingredient (D) the froth usually collapses almost immediatelyafter being generated, and the cured product consists essentially of anelastomer that may contain only a few widely spaced bubbles resultingfrom entrapped blowing agent.

The foam stabilizers (D) are resinous, benzene-soluble organosiloxanecopolymers wherein the repeating units include, but are not limited to,SiO_(4/2) units, (CH₃)₃ SiO_(1/2) units and fluorine-containing unitscomprising at least four perfluorinated carbon atoms. Each of thefluorine-containing units also includes one or two silicon atoms thatare bonded to the fluorine-containing carbon atoms by means of carbonatoms and optionally an oxygen atom as described hereinbelow.

The fluorine-containing units of (D) exhibit the formula R_(a) R_(b)'SiO.sub.(4-a-b)/2 or R"[Si(R')_(b) O.sub.(3-b)/2 ]₂. In these formulaeR and R" represent, respectively, monovalent and divalent organicradicals, each of which contains at least four perfluorinated carbonatoms, R' is alkyl containing from 1 to 3 carbon atoms, a is 1 or 2, bis 0, 1 or 2 and the sum of a and b is 3 or less. The free valences of Rand R" are bonded to the silicon atoms of the foregoing formulae by asequence of at least two methylene, i.e. --CH₂ -- units or by asilicon-bonded oxygen atom that is, in turn, bonded to a sequence of atleast two methylene units.

In addition to at least four perfluorinated carbon atoms and at leasttwo nonfluorinated carbon atoms, R and R" can include partiallyfluorinated carbon atoms. The carbon atoms of R and R" can be present inthe form of linear chains, branched chains or carboxylic rings.Alternatively, R and R" can comprise two or more groups of fluorinatedcarbon atoms or combinations of fluorinated and nonfluorinated carbonatoms. These groups and combinations are connected together either byatoms such as nitrogen, oxygen or sulfur or by divalent groups such ascarbonyl, amido, carboalkoxy, and other groups which do not hydrolyzereadily, will not cause premature curing of the present foamablecompositions during storage and will not substantially inhibit curing ofthe compositions. R and R" can contain from 4 to 20 or more carbonatoms, but preferably contain from 4 to 16 carbon atoms.

The relative concentrations of (CH₃)₃ SiO_(1/2), fluorinated siloxaneunits and any additional units other than SiO_(4/2) units and hydroxylgroups must be within certain limits for (D) to function effectively.These limits are most conveniently expressed in terms of their effect onthe surface tension of a solution of (D) in a trimethylsiloxy endblockedpolydimethylsiloxane and on the solubility of (D) in this medium.

Specifically, a 10% by weight solution of (D) in a trimethylsiloxyendblocked polydimethylsiloxane exhibiting a viscosity of 0.01 Pa.s at25° C. should exhibit a surface tension of less than 2.2×1O⁻⁴ newtonsper centimeter at 25° C. Furthermore, at this same concentration leveland temperature the solution must either be clear initially or becomeclear following the addition of not more than 100%, based on the weightof said solution, of xylene.

While not wishing to be bound by any theory, it appears that effectivefoam stabilizers decrease the surface tension of a foamable compositionand exhibit only limited solubility in the composition. The low degreeof solubility ensures that at least a portion of the stabilizer will bepresent at liquid-air interfaces of the cellular structure of the frothformed by the action of the blowing agent on the composition, therebyreducing the surface tension at the liquid-air interfaces and increasingthe stability of the froth during the curing reaction. The relativelyhigh viscosity of the present foam stabilizers is believed to impartadditional stability to the froth during curing by increasing theelasticity of the cell walls and also reducing the rate at which uncuredliquid drains from the foam.

The molar ratio of all units other than hydroxyl and SiO_(4/2) units toSiO_(4/2) units in (D) is from 0.7:1 to 1.1:1, inclusive. Preferablythis ratio is from 0.7:1 to 0.9:1, inclusive, to maximize the efficacyof (D) as a foam stabilizer for the preferred formable compositionsdisclosed in the accompanying examples.

If the foamable compositions contain acidic materials, it is usuallydesirable to employ foam stabilizers wherein the R and R" radicals ofthe foregoing formulae are bonded to silicon through a carbon atomrather than through an oxygen atom. The reason for this preference isthat silicon oxygen bonds are apparently more susceptible to cleaving inthe presence of acids than silicon carbon bonds. This cleaving appearsto destroy or substantially diminish the efficacy of ingredient (D) as afoam stabilizer.

In addition to the silicon-containing units disclosed hereinbefore, (D)typically contains from 0.2 up to about 4.0% by weight of silicon-bondedhydroxyl groups. (D) can optionally contain up to about 10 weightpercent of GSiO_(3/2) units, where G represents the residue obtained byremoving the hydrogen atom from a hydroxyl group of a hydroxylcontaining linear organic polymer. Useful organic polymers includepolyalkylene glycols, homopolymers of ethylenically unsaturated alcoholssuch as allyl and cinnamyl alcohol, copolymers of these alcohols withethylenically unsaturated hydrocarbons such as styrene. Preferredpolymers include styrene/allyl alcohol copolymers and polyethyleneglycols.

The presence of GSiO_(3/2) units apparently reduces the solubility of(D) in (A) to a level at which (D) will function more effectively as astabilizer. The presence of GSiO_(3/2) units is desirable in thoseinstances when the amount of fluorine required to reduce the surfacetension of (A) to less than 2.2×10⁻⁴ newtons per centimeter at 25° C. isinsufficient to reduce the solubility of (D) in (A) to the extentrequired for optimum foam stabilization. Because in many instanceshydroxyl-containing organic polymers corresponding to the formula GH areconsiderably less expensive than the fluorine-containing intermediatesused to prepare (D), it is usually economically preferable to employthese organic polymers in place of additional fluorine-containingintermediate to decrease the solubility of (D) in (A).

Resinous copolymers corresponding to the foregoing definition of (D) canbe prepared using methods previously disclosed for the preparation ofsimilar copolymers. For example, trimethylchlorosilane in combinationwith (1) a fluorine-containing silane of the formula R_(a) R_(b) 'SiClwhere the sum of a and b is 3, (2) a silane of the formulaR"[Si(R₂)Cl]₂, or (3) suitable derivatives of either (1) or (2) whereinthe chlorine atoms are replaced by other hydrolyzable groups, can bereacted with an aqueous solution of sodium silicate as described byDaudt et al. in U.S. Pat. No. 2,676,182, issued on Apr. 20, 1954. Thedisclosure of this patent is incorporated herein in its entirety byreference. The reaction of fluorine-containing silanes with sodiumsilicate is disclosed in U.S. Pat. No. 3,328,349, issued on June 27,1967 to Lentz and is incorporated herein in its entirety by reference.In accordance with a combination of Lentz's and Daudt et al.'s teaching,an aqueous solution of sodium silicate (e.g. No. 9 sodium silicate soldby E. I. Dupont de Nemours and Co.) is acidified to the proper pH byadding it to a mixture of hydrochloric acid and isopropanol. Theresulting acidic silica hydrosol can then be treated with a source ofR_(a) R_(b) 'SiO.sub.( 4-a-b)/2 siloxane units, such as (R)(CH₃)₂ SiOCH₃or (R)(CH₃)₂ SiCl, and a source of (CH₃)₃ SiO_(1/2) units, such as(CH₃)₃ SiCl. These reactants are preferably first dissolved in a mixtureof isopropanol and xylene. lf chlorosilanes are used, acidification ofthe sodium silicate may not be required.

After being heated for the time interval required to substantiallycomplete the reaction, the resultant mixture is cooled, whereupon itseparates into an aqueous phase, which is discarded, and a nonaqueousphase containing the resinous copolymer. The nonaqueous phase is washedwith water to reduce its acid number and remove water-solubleingredients, such as isopropyl alcohol. Preferably the resinouscopolymers prepared by this method are washed with water to remove most,but not all of the acid. The products typically have sufficient acid toprovide an acid number of from 0.2 to 2.0.

The fluorinated silanes and siloxanes that can be used to prepare (D)are either known or can be synthesized using known methods. Thesynthesis of preferred silanes is described in the accompanyingexamples.

If organic solvents are used as diluents during preparation of a foamstabilizer (D), these are preferably replaced with a trimethylsiloxyendblocked polydimethylsiloxane exhibiting a viscosity of from about0.001 to about 1 Pa.s at 25° C.

If it is desired to incorporate repeating units of the foregoingGSiO_(3/2) type into the copolymer, this can be accomplished byincluding the corresponding hydroxyl-containing polymer GH in thereaction mixture together with the fluorinated reactant. Suitablepolymers have been discussed hereinbefore.

A second type of foam stabilizer can be prepared using nonfluorinatedresinous copolymers of the type described in the aforementioned Daudt etal. patent. These copolymers contain (CH₃)₃ SiO_(1/2) and SiO_(4/2)units in addition to from 0.5 to 4.0% weight percent of silicon-bondedhydroxyl groups. The copolymers are reacted with a silane of the formulaR_(a) R_(b) 'SiY.sub.( 4-a-b) or Y(R')₂ SiR"Si(R')₂ Y, partialhydrolysis products of these silanes or a fluorine-containing alcohol ofthe formula F(CF₂)_(n) (CH₂)₂ OH where R, R', R", a and b are definedhereinbefore, Y is a halogen or other hydrolyzable group, and n is aninteger from 4 to 20. Most preferably Y is chlorine, based on theavailability of the silanes.

In preferred embodiments of (D), R of the foregoing formula representsF(C_(n) F_(2n))(CH₂)₂ O_(c), R' is methyl, R" represents --O_(c) (CH₂)₂(C_(n) F_(2n)) (CH₂)₂ O_(c) --, c is 0 or 1, and n is at least 4. Mostpreferably n is an even integer from 4 to 14 inclusive.

The silanes employed to prepare preferred embodiments of (D) wherein cof the foregoing formulae is 0 exhibit the formulae F(C_(n) F_(2n))CH₂CH₂ Si(CH₃)_(b) Y_(3-b) or Y_(3-b) (CH₃)_(b) SiCH₂ CH₂ (C_(n) F_(2n))CH₂CH₂ Si(CH₃)_(b) Y_(3-b) where b is 0, 1 or 2 and Y and n are as definedhereinbefore. These silanes can be prepared by hydrosilation of afluorinated olefin of the formula F(CF₂)_(n) CH═CH₂ or CH₂ ═CH(CF₂)_(n)CH═CH₂ with a silane of the formula (CH₃)_(b) Y_(3-b) SiH where Y and nare as defined hereinbefore. The hydrosilation reaction is typicallycarried out at temperatures of from 150° to 300° C. using as thecatalyst an organic peroxide or a platinum-containing material such aschloroplatinic acid. The hydrosilation of fluorinated olefins isdisclosed, for example, in U.S. Pat. No. 3,620,992, issued to Kim andPierce on Nov. 16, 1971 and is incorporated herein in its entirety byreference. Reaction products of fluorinated silanes and theaforementioned resinous copolymers are disclosed in the copending U.S.patent applications of Thomas Lim and Antony Wright, Ser. No. 664,917,and Chi-Long Lee, Thomas Lim and Antony Wright, Ser. No. 664,897, bothof which were filed on Oct. 26, 1984.

Alcohols employed to prepare preferred stabilizers wherein c of theforegoing formula is 1, exhibit the formula F(CF₂)_(n) CH₂ CH₂ OH. Oneexample of this class of alcohols is commercially available as a mixtureof homologs wherein the value of n is 4, 6, 8, 10 and 12. Preferred foamstabilizers of this type are disclosed and claimed in U.S. patentapplication Ser. No. 664,598, filed in the name of Joseph W. Keil onOct. 26, 1984.

A reaction between a fluorine-containing alcohol and a resinouscopolymer containing (CH₃)₃ SiO_(1/2) and SiO_(4/2) units can beconducted by dissolving the two reactants in a suitable solvent andheating the resultant solution in the presence of a catalyst forcondensation reactions of silicon-bonded hydroxyl groups while removingthe water generated as a by-product of the reaction. Catalysts for thistype of reaction include alkali metal hydroxides, organosulfonic acidsand organic or inorganic tin compounds such as stannous octoate anddibutyltin dilaurate. The reaction is preferably conducted at theboiling point of the reaction medium, which is typically a liquidhydrocarbon that forms an azeotrope with the by-product water. Otherorganic solvents such as ketones can be included to increase thesolubility of the reactants in the reaction medium.

The foam stabilizer (D) typically constitutes from 0.2 to about 25% byweight of the present foamable compositions. This value is preferablyfrom 1 to 10% by weight. The minimum concentration of (D) that willadequately maintain the structure of the initially produced liquid frothduring curing is a function of several variables, including viscosity ofthe foamable composition, the rate at which the composition cures andthe fluorine content of (D). As the fluorine content of (D) increases,it becomes less compatible with the other ingredients of the presentfoamable compositions, and is more likely to migrate to the surface ofthe bubbles that constitute the froth formed when the composition isdispensed from the pressurized container in which it is stored. Theoptimum concentration value for (D) will be within the 0.2 to 25 weight% range that characterizes the present compositions.

Moisture curable polyorganosiloxane compositions that include aliquified blowing agent and preferred embodiments of the foam stabilizer(D) are disclosed in copending U.S. patent application Ser. No. 665,272,filed on Oct. 26, 1984 in the names of Chi-Long Lee and James A. Rabe.The present compositions differ from the ones disclosed in thiscopending application in that the present compositions are curable by aplatinum- or rhodium-catalyzed hydrosilation reaction that does notrequire atmospheric moisture.

The foamable polyorganosiloxane compositions of this invention areconverted to foams by the action of a blowing agent, referred tohereinafter as (E). The blowing agent is packaged in apressure-resistant container such as an aerosol can. When the blowingagent is combined with the other ingredients of the present compositionsunder atmospheric pressure, the composition is converted to a froth thatcures to a solid, elastomeric foam at room temperature if ingredient (C)is a platinum-containing catalyst in the absence of an inhibitor. Ifingredient (C) is either a rhodium-containing catalyst or aplatinum-containing catalyst in the presence of ingredient (F), thefroth has to be heated to cure into a solid, elastomeric foam.

Ingredient (E) can be any material that is a gas at 25° C. underatmospheric pressure, can be compressed or liquified under moderatepressures and is unreactive with the other ingredients of the presentcompositions. Suitable liquifiable blowing agents include aliphatichydrocarbons containing three or four carbon atoms, dimethylether,fluorocarbons and the various chlorofluoromethanes. Isobutane isparticularly preferred on the basis of its cost and availability.Fluorocarbons and chlorofluoromethanes have been considered undesirablefor ecological reasons in the United States. Compressible gases such asair and nitrogen are also suitable blowing agents.

Ingredient (E) can constitute from about 4 to about 85% of the totalweight of the present foamable compositions. The optimum concentrationrange is dependent upon a number of variables, the most influential ofwhich appears to be the viscosity of the foamable composition, which is,in turn, dependent to a large extent upon the viscosity of (A) and theamount of any silica or other filler(s) present.

The optimum concentration of (E) is one that will provide the bestbalance between stability of the froth during curing, a sufficientlyrapid discharge rate of the composition from the aerosol can(s) or otherpressurized container(s) in which it is stored and the desire to achievea low density in the cured foam.

Too high a concentration of blowing agent may destroy the cellularstructure of the initial froth. Too low a concentration will yield ahigh density foam and decrease the maximum rate at which the ingredientsof the present composition that are stored together with the blowingagent can be dispensed from a pressurized container.

When ingredients (A) and (B) are mixed with a platinum-containingcatalyst the mixture will cure immediately at room temperature. To avoidthis premature curing during storage, ingredients (A) and (B) have to bestored in separate containers (aerosol cans) or in separate compartmentsof a two-compartment aerosol can. Ingredient (C) can be incorporatedtogether with either ingredient (A) or ingredient (B). Ingredient (D)can be incorporated in either ingredient (A) or/and ingredient (B). Theresultant product is a two-part composition. To produce a satisfactorycured foam, the two parts of the composition must be combined in aspecified volume ratio. This ratio is conveniently 1:1.

Premature curing of a one-part composition can be avoided by addition ofan inhibitor, referred to hereinafter as ingredient (F) in an amountsuch that the resultant mixture becomes stable at temperatures belowabout 60° C.

The inhibitor should not adversely affect the ability of the catalyst topromote curing at temperatures of 50° C. and above.

One suitable type of platinum catalyst inhibitor is described in U.S.Pat. No. 3,445,420, issued to Kookootsedes et al. on May 20, 1969 and ishereby incorporated by reference to show certain acetylenic inhibitorsand their use. A preferred class of acetylenic inhibitors are theacetylenic alcohols, especially 2-methyl-3-butyn-2-ol.

An optimum inhibitor concentration will provide the desired storagestability without excessively prolonging the time interval required tocure the compositions at temperatures of 50° C. and above. This amountwill vary widely, depending upon the particular inhibitor selected, thetype and concentration of the platinum-containing catalyst and thecomposition of ingredients (A) and (B).

Inhibitor concentrations as low as one mole of inhibitor per mole ofplatinum will in some instances yield a satisfactory level of storagestability and desirably short curing period. In other cases, inhibitorconcentrations of up to 500 or more moles per mole of platinum may beneeded. The optimum concentration for a particular inhibitor in a givencomposition can be determined by routine experimentation.

No inhibitor is required using rhodium-containing hydrosilationcatalysts, which typically function only at temperatures above about 50°C.

Using of one of the rhodium or inhibited platinum catalysts describedhereinbefore, all of the ingredients of a foamable composition can bepackaged in a single pressure resistant container such as an aerosol canand stored at temperatures up to 50° C. until such time as it is desiredto prepare a foam, at which time the ingredients are discharged into anarea under atmospheric pressure. At temperatures above about 0° C., theblowing agent volatilizes within the composition to form a cellular foamstructure that is maintained by the foam stabilizer (D) until the foamis cured by heating it to a temperature that is sufficiently high toactivate the inhibited catalyst. Typically this temperature is at least50° C. Heating of the foam can be accomplished by placing it in orpassing it through a heated chamber such as an oven or by exposing thefoam to infra-red radiation.

A preferred curing method involves exposing the foam to microwaveenergy. Such a method is most effective when a microwave sensitivematerial is incorporated into the foamable composition. Thesemicrowave-sensitive materials are referred to hereinbefore as optionalingredient (G). Any of the known microwave-sensitive materials can beused, so long as they do not cause premature curing of the compositionor adversely affect the ability of the composition to cure at elevatedtemperatures. The ability of materials to convert the energy present inelectromagnetic waves into heat is directly proportional to their lossfactor, referred to as "tan delta" in the art. Materials with relativelyhigh loss factors include hydroxyl-containing organic compounds such asmethanol, ethylene glycol and glycerol. Carbon black, calcium carbonateand metal oxides such as ferric oxide are also classified as microwavesensitive materials.

Organic microwave sensitive materials include copolymers containingorganosiloxane units and units derived from the polymerization oforganic compounds with polar groups such as carboxyl. A preferred classof copolymers are prepared by the peroxide catalyzed polymerization ofethylenically unsaturated polar organic compounds in the presence ofhydroxyl endblocked polydimethylsiloxanes. Useful organic monomersinclude esters of acrylic and methacrylic acids. U.S. Pat. No.4,011,197, issued to Lee on Mar. 8, 1977, discloses a method for curingnon-cellular organosiloxane compositions using the heat generated byexposing the compositions to microwave energy. The organosiloxanecompositions contain a minimum of about 5 weight % of at least onemember of a specified group of hydrocarbon radicals that includeshalogen-, sulfur-, and oxygen-containing hydrocarbon radicals and arylradicals.

The use of microwave radiation to generate the heat required to activatean inhibited platinum catalyst in a foamable composition comprising apolyorganosiloxane gum stock, an organohydrogensiloxane and a source ofhydroxyl groups is disclosed in U.S. Pat. No. 4,026,844, issued toKittle and Ronk on May 31, 1977. These compositions are based on gumstocks exhibiting a Williams plasticity value greater than 0.076 cm.

The concentration of microwave-sensitive material present in a foamablecomposition will depend upon the desired curing temperature and the lossfactor of the particular microwave-sensitive material being used.Typically, ingredient (G) constitutes from 0.5 to 60 percent by weightof foamable composition of this invention. Preferably the range is from5 to 45 percent by weight.

In addition to the aforementioned ingredients (A)-(F), the presentfoamable compositions can contain reinforcing or nonreinforcing fillers,pigments, flame retardants, antioxidants and other additivesconventionally used in polyorganosiloxane compositions. These additivesmust not adversely affect curing of the foam or the action of the foamstabilizer (D) to any appreciable extent.

The foamable compositions of this invention can optionally contain up to50% by weight, based on the total weight of the composition, of finelydivided fillers such as silica that are conventionally employed in RTVpolyorganosiloxane compositions.

Fume silicas are preferably used at concentrations of from 10 to 20%,based on the weight of the foamable composition.

Finely divided silica fillers are typically treated with relatively lowmolecular weight, liquid hydroxyl containing organic or organosiliconcompounds to prevent a phenomenon referred to in the art as"crepe-hardening" of polyorganosiloxane compositions. The fillerparticles can be treated before being added to the composition or theparticles can be treated "in situ" by having a suitable treatingmaterial present as an ingredient in the compositions. Known fillertreating agents include hydroxyl-containing silanes andpolydiorganosiloxanes where the hydrocarbon groups present on siliconare lower alkyl such as methyl, and can also include phenyl, vinyl and3,3,3-trifluoropropyl.

Other useful fillers include chopped and flocked glass fibers and flameblown glass microfibers. The glass fibers are preferably less than about8 mm long and less than about 5×10⁻³ mm in diameter Larger diameterfibers can be used, but are not as effective in modifying the flowproperties of the foamable composition as the preferred fibers. Thelarger fibers may also interfere with dispensing of the compositionthrough conventional aerosol valves by clogging passages within thevalve.

If a black or grey foam is acceptable, up to about 30% by weight, basedon the foamable composition, of carbon black can be added in place of orin combination with glass or other types of fibers.

Compositions containing silica in combination with glass fibers and/orcarbon black will be nonslumping when used in combination with liquifiedblowing agents such as isobutane or chlorinated fluorocarbons such astrifluorochloromethane. A nonslumping composition will not flowappreciably when dispensed onto a vertical or a sloping surface. Thischaracteristic is very desirable if the present compositions are used tofill joints or other open spaces in a vertical member such as a wall, orin the lower surface of a horizontally oriented member such as theceiling of a building or other structure.

In the absence of one of the aforementioned optional catalyst inhibitors(Ingredient F), compositions containing a platinum catalyst usuallybegin to cure when ingredients (A), (B) and (C) are combined.Compositions containing an uninhibited platinum catalyst must be storedin a manner that avoids contact between the organohydrogensiloxane (B)and the catalyst (C) until it is desired to react (A) and (B) andprepare a foam. So long as (B) and (C) are not present in the samemixture, the ingredients of foamable compositions that include anuninhibited platinum hydrosilation catalyst can be combined and storedfor extended periods of time in two or more parts. At the time a foam isto be formed the various parts of the composition are combined in theproper proportions, blended and discharged into an area underatmospheric pressure. As disclosed hereinbefore, the relative amounts of(A) and (B) should be equivalent to from 1 to 3 silicon-bonded hydrogenatoms in (B) per vinyl radical in (A). If any other material containingvinyl or other ethylenically unsaturated hydrocarbon radical or hydroxylgroups is present in the foamable composition, the concentration of (B)must be increased to provide a sufficient number of silicon-bondedhydrogen atoms to react with these ethylenically unsaturated radicalsand hydroxyl groups.

In accordance with a preferred method for packaging a two-part foamablecomposition of this invention, at least a portion of ingredient (A), thediorganovinylsiloxy endblocked polydimethylsiloxane, is combined withingredient (B), the organohydrogensiloxane and the foam stabilizer (D).The remainder of ingredient (A) can be combined with the catalyst (C)and foam stabilizer (D).

The blowing agent can be present in one or both of the aforementionedportions or it can be added when the other ingredients of the presentcomposition are combined to form a foam. Because the blowing agent (E)is a gas at temperatures above 0° C. under atmospheric pressure, anycombination of ingredients that includes (E) should be stored in aclosed, pressure-resistant container. Preferably the two portions of thepresent composition are each packaged together with blowing agent inpressurized containers such as aerosol cans. In this instance theblowing agent also acts as a propellant to expel each part of thecomposition from the container in which it is stored. In a preferreddispensing system both containers are equipped with suitable aerosoltype valves which discharge into a common conduit that preferablyincorporates a means for homogeneously blending the contents of the twocontainers prior to discharging the resultant mixture as a froth into anarea under atmospheric pressure. The ingredients of the composition canbe blended using various means that have been disclosed in the priorart. A preferred means comprises a static mixer consisting of a tubehaving baffles arranged along the interior surface that generate theturbulence required to achieve adequate mixing of materials passingthrough the tube.

Methods and equipment for packaging compositions containing volatilematerials into pressure-resistant containers are well known in the artand do not form part of this invention.

Alternatively, two-part compositions can be packaged in atwo-compartment container equipped with a codispensing valve havingaccess to both compartments of the container. Valves of this type arecommercially available.

If the composition is very viscous and/or contains a filler that impedesflow of the composition through the valve of the pressurized container,it may be desirable to package the compositions in a two-compartment canwherein only one compartment is equipped with a valve and contains atleast a portion of the foamable composition, including the blowingagent. The second compartment is separated from the first by means of apiston or a flexible wall and contains a propellant that can be of thesame composition as the blowing agent or can be a more volatilematerial. The propellant provides the additional pressure required toincrease the rate at which the foamable composition can be dispensedfrom the pressurized container. Two-compartment aerosol cans are knownin the art and can be equipped with any of the known types of aerosolvalves and spray heads.

All other conditions being equal, the maximum rate at which a foamablecomposition of this invention can be dispensed from a pressurizedcontainer and the rate at which liquid materials will drain duringcuring of the foam are both inversely proportional to the viscosity ofthe foamable composition. To obtain useful foams the viscosity of thecomposition should be at least 0.5 Pa.s at 25° C. The optimumcombination of a relatively rapid dispensing rate and stability of theresultant cellular structure during curing is achieved without anexcessive amount of blowing agent when the viscosity of the foamablecomposition is from 1 to 100 pa.s at 25° C.

If it is desired to prepare foams on a large scale without the necessityof storing combinations of ingredients, ingredients (A), (B), (C), (D)and, optionally, (F) together with any additional ingredients other thanthe blowing agent are dispensed from their individual containers and theliquified blowing agent (E) is dispensed from a pressurized container.The ingredients are blended in a suitable pressurizable mixing head andthe resultant foam is dispensed at the outlet of the mixing head.

Foams prepared from one-part foamable compositions containing amicrowave sensitive material are cured by exposing them to a source ofmicrowave radiation, which is typically above a frequency of 1000 MHz.The duration of the exposure is dependent upon the type ofmicrowave-sensitive material and the intensity of the radiation absorbedby the composition. Typically a foam can be cured in from 5 to 20minutes. Microwave radiation can completely penetrate the foamedcomposition, thereby making it possible to cure the interior portion ofthick foams relatively quickly.

The use of microwave radiation makes possible the dispensing and curingof foamable compositions in areas where conventional heating means suchas electric or gas fired ovens are not practical. Unlike conventionalheating means, the microwave source does not become heated and can bereadily transferred or handled once supplying of electrical power to thesource is discontinued.

A variety of microwave generators are known, and many are commerciallyavailable. A preferred generator is a microwave oven of the typeconventionally used for food preparation.

The foam stabilizer (D) will maintain the cellular structure of theresultant uncured froth, however it usually cannot entirely stop thedrainage of liquid material and the gradual collapse of the froth. lt istherefore recommended that microwave curable foamable compositions becured as soon as possible after being dispensed.

The foams generated using the present foamable compositions are of theclosed cell type and useful in numerous applications, includinginsulation, packaging material and as caulking material to fill gaps andconduits in buildings and transportation vehicles. The density of thefoams is within the range from 0.1 to 0.5 g/cm³, making them moreeconomical than conventional noncellular polyorganosiloxane compositionstypically used as sealants. The size of the cells is within the range offrom less than 0.5 mm up to 5 mm.

The following examples disclose preferred foamable compositions that arewithin the scope of the accompanying claims, and should not beinterpreted as limiting the scope thereof. All parts and percentages areby weight unless otherwise specified.

EXAMPLE 1

This example demonstrates formation of a microwave curable foam using aone-part composition of this invention containing calcium carbonate asthe microwave-sensitive material.

The foam stabilizer (D) used in this example and Example 2 was preparedby the reaction of a resinous organosiloxane copolymer with afluorinated alcohol.

A glass reactor equipped with a thermometer, reflux condenser,mechanically driven stirrer and Dean-Stark apparatus to retain a portionof the condensate returning to the reactor, was charged with 60.5 partsof a 74.4% solution in xylene of a resinous organosiloxane copolymer,5.0 parts of a mixture of homologous fluoroalcohols having the averageformula F(CF₂)₈ CH₂ CH₂ OH and available as Zonyl® BA Fluoroalcohol,34.3 parts of xylene and 0.25 part of a 1 N solution of potassiumhydroxide in ethanol. The organosiloxane copolymer consisted essentiallyof repeating units of the formulae (CH₃)₃ SiO_(1/2) and SiO_(4/2) in amolar ratio of about 0.75:1.0, respectively and contained about 2.5% byweight of silicon-bonded hydroxyl groups. The copolymer is described inthe aforementioned U.S. Pat. No. 2,676,182 to Daudt et al.

The contents of the reactor were heated at the boiling point for 11/2hours, then cooled to 50° C. and neutralized to a pH of about 7 bybubbling carbon dioxide through the reaction mixture. The resultantmixture was then combined with 50 parts of a trimethylsiloxy endblockedpolydimethylsiloxane exhibiting a viscosity of 0.01 Pa.s and thevolatile materials were then evaporated under reduced pressure. Theresultant clear solution exhibited a surface tension of 1.92×10⁻⁴newtons/cm.

A microwave curable, foamable composition of this invention was preparedby blending together equal weights of calcium carbonate and adimethylvinylsiloxy endblocked polydimethylsiloxane exhibiting aviscosity of about 0.4 Pa.s at 25° C. One hundred parts of the resultantmixture was placed in an aerosol can, followed by 2.06 parts of atrimethylsiloxy endblocked dimethylsiloxane/methylhydrogen-siloxanecopolymer containing 0.8 percent by weight of silicon-bonded hydrogenatoms, 2.63 parts of the foam stabilizer prepared as described in thefirst part of this Example and 0.5 part 2-methyl-3-butyn-2-ol as thecatalyst inhibitor. The resultant mixture was thoroughly blended, atwhich time there was added 0.19 part of a chloroplatinic acid complex ofsymmetrical tetramethyldivinyldisiloxane diluted with sufficient liquiddimethylvinylsiloxy endblocked polydimethylsiloxane to achieve aplatinum content of about 0.7 weight percent. The cover and valveassembly of the aerosol can were then secured in position and 9 parts ofisobutane was added through the valve. A foam-type spray head was thenplaced over the valve and the container was shaken by hand to evenlydistribute the isobutane throughout the composition.

A portion of the contents of the aerosol can was dispensed into a squarecontainer measuring 5×5 cm to yield a foam having a height of about 1.8cm. The container was then placed in a microwave oven (Magic Chef ModelNo. MW3172-5P) and exposed to microwave radiation at a frequency of 2450Mkz. for ten minutes with the intensity control at the "high" setting.The resultant white foam exhibited a smooth, non-tacky surface and adensity of 0.37 g/cc. The cells ranged in diameter from 0.5 to 5 mm andall appeared to be closed.

The foam could not be ignited when contacted with the flame of a match.

EXAMPLE 2

This example demonstrates formation of a foam using glycerine orpowdered aluminum as the microwave-sensitive material.

A first foamable composition was prepared by packaging the followingingredients in an aerosol can.

50 parts of the dimethylvinylsiloxy endblocked polydimethylsiloxane ofExample 1,

2.06 parts of the dimethylsiloxane/methyl hydrogensiloxane copolymer ofExample 1,

2.71 parts of the foam stabilizer described in Example 1

0.05 part 2-methyl-3-butyn-2-ol,

5.08 parts glycerine, and

0.2 part of the chloroplatinic acid complex of Example 1, and

7.2 parts of isobutane.

A foam was dispensed and cured as described in Example 1, with theexception that the residence time in the microwave oven was sevenminutes. Samples of the resultant cured foam exhibited densities of from0.08 to 0.17 g. per cc.

A second foamable composition was prepared using the same types andamounts of polydimethylsiloxane anddimethylsiloxane/methylhydrogensiloxane copolymer, and the same amountsof isobutane, 2-methyl-3-butyn-2-ol, and chloroplatinic acid complex asin the first composition. The second composition also contained 2.78parts of the same foam stabilizer as the first composition and 5.0 partspowdered aluminum in place of the glycerine as a microwave sensitivematerial.

The second composition was packaged in an aerosol can and dispensed as afoam. The foam was cured as described in the foregoing Example 1 using aresidence time in the microwave oven of seven minutes. The resultantclosed cell cured foam exhibited a density of 0.10 g/cc and a cell sizerange of from 0.2 to 1.5 mm.

EXAMPLE 3

Part I of a two-part foamable composition of this invention was preparedby blending to homogenity the following ingredients:

19 parts of a dimethylvinylsiloxy endblocked polydimethylsiloxane (A¹)exhibiting a viscosity of 0.4 Pa.s at 25° C.;

12 parts of a dimethylviuylsiloxy endblocked polydimethylsiloxane (A²)exhibiting a viscosity of about 30 Pa.s at 25° C.;

1.7 parts of a foam stabilizer prepared using the organosiloxanecopolymer and fluoroalcohol composition described in Example 1 and theprocedure described hereinbelow. ln this instance the weight ratio ofcopolymer to fluoroalcohol composition was 4:1 respectively;

6.5 parts of finely divided quartz having an average particle size of 5microns, and

0.34 part of a liquid catalyst composition prepared by reacting 3.6parts of chloroplatinic acid hexahydrate with 200 Parts of an oligomericdimethylvinylsiloxy endblocked polydimethylsiloxane having an average offive dimethylsiloxane units per molecule. After heating for 3.5 hours at70° C. the resultant mixture was combined with 40 parts sodiumbicarbonate and 200 parts of water and heated for 2 hours at atemperature of 60° C. The platinum content of the filtered liquidreaction product was 0.66% by weight.

Part II of the foamable composition was prepared by combining togetherthe following ingredients to form a homogeneous composition.

17 parts of polydimethylsiloxane A¹ described hereinabove,

12 parts of polydimethylsiloxane A² described hereinabove,

1.7 parts of the foam stabilizer of part I,

6.5 parts of the finely divided quartz present in Part I, and

1.33 parts of a trimethylsiloxy endblocked copolymer containing 37.5mole percent dimethylsiloxane units and 62.5 mole percentmethylhydrogensiloxane units. The content of silicon-bonded hydrogenatoms in the copolymer was between 0.7 and 0.8 percent by weight.

The foam stabilizer wa prepared by adding 20 parts of the moltenfluoroalcohol described in Example 1 to 80 parts of the copolymerdescribed in Example 1 as a 50% solution in xylene, followed by theaddition of one part of a 1N ethanolic solution of potassium hydroxide.The resultant mixture was then heated at 120°-130° C. for about 2.5hours, at which time it was allowed to cool. Solid carbon dioxide wasthen added to neutralize the basic materials present in the reactionmixture. The mixture was then combined with 100 parts of atrimethylsiloxy endblocked polydimethylsiloxane exhibiting a viscosityof 0.01 Pa.s at 25° C. The xylene and other volatile materials were thenremoved by heating the reaction mixture under reduced pressure.

The foam stabilizer contained (CH₃)₃ SiO_(1/2) and SiO_(4/2) units,silicon-bonded hydroxyl groups and fluorinated siloxane units of theformula F(CF₂)_(n) CH₂ CH₂ OSiO_(3/2) --where the average value of n is8. The molar ratio of all units in the foam stabilizer with theexception of hydroxyl groups and SiO_(4/2) units, to said SiO_(4/2)units were from 0.7:1 to 1:1, inclusive, a 10% by weight solution of thefoam stabilizer in a trimethylsiloxy polydimethylsiloxane exhibiting aviscosity of 0.01 Pa.s at 25° C. was clear and exhibited a surfacetension of less than 2.2×10⁻⁴ newton per cm at 25° C.

Compositions I and II were placed in two supply tanks of a commercialfoam machine (Model 2100-354 manufactured by Sealants Equipment andEngineering, Inc., Oak Park, Mich.). The blowing agent was a mixture of60% by volume of dichlorodifluoromethane and 40% by volume oftrichlorofluoromethane. This mixture was supplied to the nucleating airport of the foam machine by means of a metering pump and a pressurerelief valve that was set at 6900 kilopascals.

The pumps of the supply tanks containing Parts I and 11 of the foamablecomposition were adjusted to deliver equal volumes of each part to thefoam machine at a rate of 830 g per minute. Three different meteringpump settings were used. The calculated amounts of blowing agentdelivered to the foam machine were 0.175 cc per 9ram combined Parts Iand II, 0.22 cc per gram of combined Parts I and II and 0.33 cc per gramof combined Parts I and II. The calculated amounts of blowing agent werebased on a previously obtained calibration curve for the metering pump.

When an equilibrium condition had been established, as evidenced by afoam of consistent quality, the foams obtained using the threeaforementioned gas pump settings were collected individually in 947 cccapacity containers. The foams were allowed to stand for about 45minutes, after which the interior of each form was examined and thedensity measured. This information is summarized in the following table.

    ______________________________________                                              cc                                                                      Sam-  Blowing                                                                 ple   Agent    Foam                                                           Num-  per g. of                                                                              Density                                                        ber   Pts. I & II                                                                            (g/cc)   Foam Appearance                                       ______________________________________                                        1     0.175    0.47     Majority of cells smaller                                                     than 0.5 mm in diameter.                                                      Scattered cells were 2-5 mm                                                   in diameter                                           2     0.22     0.41     Majority of cells smaller                                                     than 0.5 mm, others 0.5-1 mm                                                  in diameter and larger percentage                                             of 2-5 mm cells than in Sample 1                      3     0.33     0.27     Majority of cells 0.5-1 mm                                                    in diameter, approximately                                                    as many 2-5 mm diameter cells                                                 as in Sample 2                                        ______________________________________                                    

The foregoing data demonstrate the effect of blowing agent concentrationon the cell size distribution and density in the final foam. All of thefoams cured within 5 minutes after being sprayed.

EXAMPLE 4

This example demonstrates the use of (1) a catalyst prepared using afluorinated siloxane and (2) an organohydrogensiloxane of the formula[H(CH₃)₂ SiO]₄ Si in a two-part foamable composition of this invention.

Part I' of the two-part composition was prepared by blending thefollowing ingredients to homogeneity:

30 parts of a dimethylvinylsiloxy endblocked polydimethylsiloxaneexhibiting a viscosity of 2.1 Pa.s at 25° C.,

1.7 parts of a foam stabilizer prepared as described in the precedingExample 3, and

0.14 part of a platinum-containing catalyst (C) obtained by reacting55.5 parts of a dimethylvinylsiloxy endblockedpoly(methyl-3,3,3-trifluoropropylsiloxane) containing an average ofthree fluorinated siloxane units per molecule with one part ofchloroplatininc acid hexahydrate at a temperature of 70° C. for threehours. Three parts of solid sodium bicarbonate were then added to thereaction mixture to neutralize acidic by-products, followed by a volumeof a saturated aqueous sodium bicarbonate solution equal to about halfthe volume of the reaction mixture. The non-aqueous layer was thenisolated, washed three times with distilled water and then dried usinganhydrous calcium sulfate. The product contained 0.73% platinum. It wascombined with a second reaction product prepared using the same methodand containing 0.3% platinum. The resultant mixture contained 0.52%platinum and was used as catalyst (C).

Part II' of the composition was prepared by homogeneously blending:

30 parts of the polydimethylsiloxane used to prepare Part I' of thisexample,

0.6 parts of [H(CH₃)₂ SiO]₄ Si, and

1.7 parts of the foam stabilizer used in Part I'.

Parts I' and II' were packaged individually into conventionalone-compartment aerosol cans together with 7.2 parts of isobutane as theblowing agent. The valves of the cans were connected to a common conduitthat terminated in a static mixer consisting of a tube having a networkof baffles by means of which parts I' and II' were thoroughly blendedbefore exiting from the conduit.

When the valve stems of both aerosol cans were depressed substantiallysimultaneously a liquid foam emerged from the open end of the conduit.The foam cured in two minutes at room temperature with substantially nodrainage of liquid material to yield a solid foam exhibiting a densityof 0.32 g/cc and a cell size range of from 0.1 to 0.5 mm.

For comparative purposes a composition composed of Parts I" and II" wasprepared using the same ingredients as Parts I' and II', respectively,of this example, except that the foam stabilizer was omitted. Theamounts of polydimethylsiloxane, organohydrogensiloxane and isobutanewere identical to those in Parts I' and II' and the amount of catalystwas increased from 0.14 part to 0.28 part. Parts I" and II" werepackaged in aerosol cans and dispensed as described in the first part ofthis example. Because it did not contain any foam stabilizer, the foamcollapsed immediately after being dispensed. The cured product was asolid rubber containing a few bubbles that measured from 2 to 5 mm indiameter.

That which is claimed is:
 1. A foamable polyorganosiloxane compositionexhibiting a viscosity of at least 0.5 Pa.s at 25° C., said compositionconsisting essentially of the product obtained by homogeneously blendingtogether(A) a polydimethylsiloxane containing at least two vinylradicals per molecule and exhibiting a viscosity of from 0.1 to 100 Pa.sat 25° C.; (B) an organohydrogensiloxane containing an average of atleast 3 silicon-bonded hydrogen atoms per molecule in an amountsufficient to cure said composition in the presence of a hydrosilationcatalyst; (C) a catalytically effective amount of a platinum-containinghydrosilation catalyst, (D) from 0.2 to 25%, based on the weight of saidpolyorganosiloxane composition, of a foam stabilizer consistingessentially of a resinous, benzene-soluble organosiloxane copolymercomprising SiO_(4/2) units, (CH₃)₃ SiO_(1/2) units andfluorine-containing units selected from the group consisting of R_(a)R_(b) 'SiO.sub.(4-a-b)/2 , R"[Si(R')_(b) O.sub.(3-b)/2 ]₂ andcombinations thereof, where R is a monovalent organic radical containingat least four perfluorinated carbon atoms, R' is an alkyl radicalcontaining from 1 to 3 carbon atoms, R" is a divalent organic radicalcontaining at least four perfluorinated carbon atoms, R and R" arebonded to the silicon atoms of their respective fluorine-containingunits by means of a sequence of at least two methylene radicals or asilicon-bonded oxygen atom that is, in turn, bonded to a sequence of atleast two methylene radicals, a is 1 or 2, b is 0, 1 or 2 and the sum ofa and b is 3 or less, the molar ratio of all units other than hydroxyland said SiO_(4/2) units to said SiO_(4/2) is from 0.7:1 to 1.1:1inclusive, and the molar ratio of the (CH₃)₃ SiO_(1/2) units withrespect to said fluorine-containing units and any remaining units otherthan said SiO_(4/2) units is such that(a) the surface tension exhibitedby a 10% by weight solution of (D) in a trimethylsiloxy endblockedpolydimethylsiloxane exhibiting a viscosity of 0.01 Pa.s at 25° C. isless than 2.2×10⁻⁴ newtons per cm at 25° C., and (b) said 10% by weightsolution requires the addition of from 0 to 5 weight % of xylene toachieve clarity at 25° C. and; (E) an amount of a blowing agentsufficient to convert said composition to a foam during exposure of saidcomposition to atmospheric pressure and a temperature of at least 0° C.2. A composition according to claim 1 where the organohydrogensiloxane(B) is selected from the group consisting ofpolymethylhydrogensiloxanes, dimethylsiloxane-methylhydrogensiloxanecopolymers, and [H(CH₃)₂ SiO]₄ Si.
 3. A composition according to claim 1wherein the hydrosilation catalyst (C) is a reaction product ofchloroplatinic acid with a vinyl-terminated polydiorganosiloxane of thegeneral formula (CH₂ ═CH)R₂ '"Si[OSi(CH₃)(R'")]_(x) OSiR₂ '"(CH═CH₂),where each R'" is individually selected from the group consisting ofalkyl radicals containing from 1 to 4 carbon atoms, phenyl radicals and3,3,3-trifluoropropyl radicals, and x represents an integer from 1 to 6,inclusive.
 4. A composition according to claim 1 where thepolydiorganosiloxane (A) is a dimethylvinylsiloxy endblockedpolydimethylsiloxane exhibiting a viscosity of from 0.1 to 50 Pa.s at25° C.
 5. A composition according to claim 1 where said blowing agent(E) is selected from the group consisting of an aliphatic hydrocarboncontaining three or four carbon atoms, dimethyl ether, a fluorocarbonand a chlorofluoromethane.
 6. A composition according to claim 5 wheresaid blowing agent is isobutane.
 7. A composition according to claim 1where the fluorine-containing units of (D) are of the formula R_(a)R'_(b) SiO.sub.(4-a-b)/2 where R is F(CF₂)_(n) (CH₂)₂ O_(c) ; R' ismethyl; a is 1; b is 0, 1 or 2; c is 0 or 1 and n represents at leastone even integer from 4 to 16, inclusive.
 8. A composition according toclaim 7 where b is 0 and (D) is the reaction product of anorganosiloxane copolymer consisting essentially of (CH₃)₃ SiO_(1/2)units, SiO_(4/2) units and from 0.5 to about 4.0% by weight ofsilicon-bonded hydroxyl groups with a silane of the formula [F(C_(n)F_(2n) (CH₂)₂ ](CH₃)_(b) SiCl_(3-b) where b is 1 or
 2. 9. A compositionaccording to claim 7 where b is 0, c is 1 and (D) is the reactionproduct of a mixture comprising an organosiloxane copolymer consistingessentially of (CH₃)₃ SiO_(1/2) units, SiO_(4/2) units and from 0.5 toabout 4.0% by weight of silicon-bonded hydroxyl groups with afluorine-containing alcohol of the formula F(CF₂)_(n) (CH₂)₂ OH.
 10. Acomposition according to claim 9 where (D) contains up to 10%, based onthe weight of (D), of GSiO_(3/2) units, where G represents the residueobtained by removal of a hydrogen atom from the hydroxyl group of ahydroxyl-containing organic polymer.
 11. A composition according toclaim 10 where said hydroxyl-containing organic polymer is selected fromthe group consisting of polyalkylene glycols, homopolymers ofethylenically unsaturated alcohols, and copolymers of said alcohols withethylenically unsaturated hydrocarbons.
 12. A composition according toclaim 11 where said hydroxyl-containing organic copolymer is astyrene/allyl alcohol copolymer.
 13. A composition according to claim 1where (D) constitutes from 1 to 10% of the weight of said composition.14. A polyorganosiloxane foam prepared by dispensing the composition ofclaim 1 from at least one pressurized container wherein said compositionis storage stable into an area under atmospheric pressure and atemperature of at least 25° C., and wherein the density of the curedfoam is from 0.1 to 0.5 g/cc and the cell size is within the range offrom less than 0.5 mm to 5.0 mm.
 15. A foam according to claim 14wherein the foam is allowed to cure under ambient conditions.